1. Field of the Invention
The present invention relates to an image display device for video equipment, and particularly to a support mechanism for the cathode wires in such a display device.
2. Description of the Prior Art
Cathode ray tubes (CRTs) have conventionally been used for the display element in color television monitors, but a conventional CRT is extremely deep in proportion to the screen area, and this has made it impossible to manufacture a thin television receiver. While electroluminescent display elements, plasma display elements, and liquid crystal display elements have been developed for use in flat display devices, these elements offer insufficient brightness, contrast, and color reproducibility, and the development of such elements which are practical for use in television receivers is still far off. A new video display device designed to display color television images using electron beams in a flat display device has therefore been proposed. This device divides the screen display area into multiple sectors in the vertical direction, and deflects an electron beam to each sector in the vertical direction to display multiple lines. This screen is also divided into multiple sectors horizontally; red, green, and blue (RGB) fluorescent materials in each sector are sequentially illuminated. The irradiation of the RGB materials by the electron beam is controlled by the color video signal, thus achieving a television image display element. Display devices such as these are described in U.S. Pat. Nos. 4,158,210, 4,404,493, and 4,535,272.
A conventional display device is described below with reference to FIGS. 1 and 2, in which reference number 1 is the wire cathode serving as an electron beam source; 2a and 2b are support frames which support and secure both ends of cathode wires 1; 3 is a mesh-shaped control electrode; 4 is the fluorescent material; 5 is the back electrode; 6a and 6b are the containers; and 7 is the spring which applies a tension to each cathode wire 1.
A display device so constructed operates as described below.
The wire cathodes 1, which are the electron beam source, are suspended across the display in the horizontal direction and held by flat springs 7 mounted to support frames 2a and 2b. Thus, electron beams are emitted linearly from wire cathodes 1 in the horizontal direction across the screen. Multiple cathode wires 1 are provided at an appropriate interval across the screen (only seven wires are shown in FIG. 1).
In FIG. 2, an enlarged view of the cathode wire 1 suspension construction is shown. Each of cathode wires 1 is secured by one of springs 7, which are supported by insulated support frame 2b, which in turn are mounted to back electrode 5. It is important to maintain a predetermined distance between each cathode wire 1 and control electrode 3, and also between each cathode wire 1 and back electrode 5 in order to eliminate variations in picture brightness. Therefore, an optical measuring instrument or similar device is used to monitor the pitch dimension and depth dimension while processing each of V-grooves 8 to obtain a precision of several microns. The cathode wires 1 may be of various materials, one of which is a tungsten wire 10 to 20 microns in diameter coated with an oxide cathode material. A control pulse is applied to the cathode wires 1 to generate an electron beam sequentially from each wire cathode 1 for a predetermined time period, and a heat current is applied during the intervals between the electron beam emission periods to maintain the cathode wires 1 at the temperature required for electron beam emission. Furthermore, when operation is started, the control pulse controlling electron beam emission and the heat current are applied to cathode wires 1 at the same time.
The back electrode 5 suppresses the generation of an electron beam from the cathode wires 1 other than the one which is currently producing the electron beam, and operates so that the generated electron beam is emitted in the forward direction towards the screen.
The mesh-shaped control electrode 3 has a long horizontal slit opposite each of the cathode wires 1; the electron beams are passed through these slits and simultaneously deflected vertically or horizontally by an electromagnetic field.
The fluorescent material 4 is painted in a striped pattern on the display surface of the housing in a vertical direction so that there is one pair each of the red, green, and blue fluorescent bodies for each single electron beam arrayed horizontally.
After these component materials are inserted to housing members 6a and 6b, the housing is sealed with flit or a like material, and a vacuum is formed inside the panel.
In a conventional display device as described above, it is important to maintain a predetermined spacing between the cathode wires 1 and control electrode 3, and between cathode wires 1 and back electrode 5 as previously described. Any error in this spacing may produce uneven luminance in the displayed image. According to the prior art, the V-grooves are therefore provided as previously described to control this spacing. Thus, according to the prior art, it is necessary to form grooves with high preciseness, but would result in poor productivity. In addition, because the wire contact area is great and the cathode wires 1 are extremely thin, the cathode wires 1 also break relatively easily.